Photographic relief process



Jan.'26 1931. L T. TROL'AND 2,068,819

PHOTOGRAPHIC RELIEF PROCESS Filed Sept. 9, 1935 2 Sheets-Sheet 1 PRIMARYEXPOSURE WIMARV EXP SURE co/v TACT PRINTING PENE TRA TING LIGHTDEVELOPMENT DEVELOPMENT 5/1. VER REMOVED EXPOSURE THROUGH PRIMARY RECORDSECONDARY EXPOSURE ETCHl/VG CONTRAST LIGHT DEVELOPMENT HA3 FDEN/IVG 19LEA C Hl/VG PHOTOGRAPHIC RELIEF PROCESS Filed Sept. 9, 1933 2Sheets-Sheet 2 lmunu nm l Hmmlll /l lluuuw nun nn Hug PRIMARY, EXPOSUREPRIMARY EXPOSURE RE l/ERSAL I DEVELOPMENT DEVELOP/WEN 7' B/CHROMATESENS! TlZ/NG I SECONDARY EXPOSURE WWW 5 HOT WATER DEVELOPMENT SECONDARYEXPOSURE GEL/i T/NE RELIEF Patented Jan. 26, 1937 rno'roermrmo RELIEFrnocnss Leonard T. Troland, deceased, late of Cambridge,-

Mass., by Cambridge Trust Company, executor, Cambridge, Mass., assignorto Technicolor Motion Picture Corporation, Hollywood, Calif., a

corporation of Maine Application-September 9', 1933, Serial No. 688,805

iClaims. (or. 95-51;)-

The present invention relates to photography,

and particularly to the making-of gelatine reliefs which can be dyed,(the dye being taken up in conformity with the pattern of the reliefrepresenting a record) and used in that state, or for transferring thedye, and with it the record, to another gelatine layer, by means of the-so-called imbibition printing.

Heretofore, such reliefs have, for example, been made by exposingthrough its support a silver haloid emulsion containing a lightrestraining dye, or a colloid layer made sensitive with a chromiumcompound. The exposed portion of the silver emulsion can be hardened insome manner, for example with a hardening developer, and/or in ahardening and bleaching bath, Whereas a chromium emulsion is hardened bythe exposure itself. In either case, the thickness of the exposedemulsion layer varies in accordance .with the strength of the exposurelight, and by removing the unexposed portion of the emulsion at theouter emulsion surface, a record bearing gelatine relief can beobtained. Among other disadvantages, these and similar methods requireexposure through the support and therefore copying from the negativerecordswith the aid of projection printers involving certaindifficulties well known in the art. It has therefore.

been proposed to print upon a silver haloid emulsion from the front orentrant side, and to obtain a record near the support by meansof thewell known so-called reversal process .which involves development of theexposed outer portions of the emulsion-with a non-hardening developer,re-exposing the emulsion to uniform light, thereby exhausting the silverhaloid contents thereof, developing and hardening these not yetdeveloped but re-exposed portions of the gelatine and removing theouter, unhardened portion, so that the inner portion remains,constituting a relief which inversely corresponds to the record obtainedwith the first exposure.

In contradistinction to this known method, the relief process accordingto the present invention proposes in its main aspect not merely anauxiliary over-all exposure of undeveloped gelatine,

but an auxiliary exposure of a sensitive emulsionthrough a recordobtained with a primary exposure and contained in the emulsion itself.

It is one important feature of the invention that it permits, due tothis peculiar procedure, a better control of the final record, since itprovides two record controlled exposures by which the photographiccharacteristics of the final relief record can be controlled,

' The latent primary record is then developed and, if desired, changedand corrected. Another object is to provide a process resulting ingelatine reliefs of especially fine grain due to an auxiliary exposurecontrolled by a record not containing the larger grains or particles ofits silver emulsion.

In another aspect, the invention in one of its modifications permits, inaddition to some or all of the herein named objects, the commercialutilization of chromate emulsions for relief. making, which emulsionscould heretofore not be 1 employed to advantage due to their extremelylow sensitivity to light, making it impracticable to use such emulsionsfor the printing of motion picture records by ordinary means.

In still another aspect, the invention permits the use of an emulsionnot containing a light restraining dye for the initial record impartingexposures,'and therefore a much quicker and therefore more economicalprinting.

These and other objects and advantages of the 20 invention will beapparent from the following explanation of its general aspect as well asof several embodiments thereof illustrating its genus. The descriptionrefers to drawings in which:

Fig. 1 is a diagrammatic flow chart of the gen- 2 eral aspect of theinvention;

Fig. 2 is a similar chart'of one embodiment of the invention; and

Figs. 3 and 4 are such charts illustrating another embodiment intwodifferent modifications.

In its general aspect, the method according to the invention involvesthe following steps illus-, trated in Fig. 1. To a customary silverhaloid emulsion E on support S is in some way imparted a latent recordPL indicated in Fig. 1 by stipppling to various densities and hereinreferred to as primary record. Although this record is indicated in Fig.1 as uniformly penetrating the entire emulsion (presupposing atheoretically transparent emulsion made up of grains ofvaryingsensitivity) it will be understood that in actual practice thislatent record, may be more or less concentrated towards one emulsionsurface.

and the emulsion, which is maintained sensitive. by utilizing itsremaining sensitivity or by resensitizing, thereuponsubjected to anauxiliary exposure through the support, the penetration of this secondexposurebeing' controlled bythe primary record PR and reaching to depthsindicatedby line a. The second exposure is 'controlled, and restrictedto the emulsion strata towards the support by using emulsions andexposure light-of contrasting colors, in a manner well known in itselffor obtaining concentrated records. The emulsion is then againdeveloped, the gelatine portion between the support and line a hardened,and the remaining outer and unhardened gelatine portion removed oretched off by known means, whereupon a gelatine relief R remains whichis inverse of the primary record PR, that is, a positive if PR was anegative, or vice versa. The relief can now be further utilized in wellknown manner, as previously indicated. In actual practice, thisprocedure can be carried out in various ways, some of which will now bedescribed in detail.

According to the embodiment outlined in Fig. 2, an undyed silveremulsionE is exposed by contact printing to a master positive M, thisprimary exposure providing a latent record PL. Preferably, the exposureis made with light that is not strongly absorbed by the emulsion, suchas green or yellow light, herein also referred to as penetrating lightin contradistinction to contrast light. The emulsion E is then developedwith a nonhardening, for example, a metol developer, preferably to ahigh gamma. It will be evident that this procedure exposes andeliminates from further activity all larger and therefore high sensitivegrains practically throughout the emulsion, and produces a recordsubstantially extending through the entire depth of the emulsion andmainly made up by silver grains whose size varies according to therecord pattern, the parts which received the highest exposure having thegreatest number of exposure affected and developed grains.

The developed silver is then removed, as for example, with the followingwell known bleaching bath:

This solution is then washed out, or neutralized with a suitable alkali.The film, always retained 'inthe dark room, is then preferably dyed witha dye, as for example xylene yellow (Colour Index #639) which increasesits absorption of actinic rays. The emulsion is then exposed, throughthe support, to uniform light preferably of contrasting color, asviolet, the hues of light restraining dye and secondary exposure lightbeing regulated to produce a secondary record SR of desired density andthickness. It is evident that the effect of the secondary exposurelight, controlled, in the sense of being limited and determined, by theremaining record made up of unaffected silver haloid grains and by therestraining dye, will be an exposure of the grains substantially betweenthe support and line b, the larger grains being already eliminated aspointed out above. The film is now-again developed, preferabl to a highdegree (in order to reduce all exposed grains between line b andsupport) and with a hardening developer (for example, according toPatent No. 1,535,700 to L. T. Troland, of April 25, 1925), fixed,washed, and bleached in one of the solutions well known for thispurpose, for example:

cc. Potassium bichromate 6 Hydrochloric acid 10 Water 1000 Thereupon,the unhardened gelatine A intermediateline b and the outer emulsionsurface is dissolved with water of approximately 140. F.,

and the film dried, the remaining relief R representing the gradationsof the original negative from which master positive. M was made.

It will now be apparent, that this process permits flexible control ofthe gamma at two points, namely during the exposure to the masterpositive, and by means of adjusting the light absorption during thesecondary exposure. Further, as already pointed out, the secondary imagehas a fine grain structure due to the fact that the primary exposureeliminates the larger, more sens".- tive grains, leaving the smallerones to form the relief image. Still further, it will now also beapparent that the photographic speed of the primary exposure of theundyed emulsion, in a printing machine, can be much greater, and theprocess therefore cheaper, than with the commonly used initially dyedemulsions, the duration of the secondary exposure being of courseimmaterial since it merely involves exposure to uniform light.

It will be further noted that this process is not appreciably affected'by variations in emulsion thickness, sincethe altitude or maximum lightof the final relief is primarily determined by the secondary, and notthe primary exposure; providing that, as above described, the light ofthe primary exposure is not substantially absorbed within the emulsion.

However, it may sometimes be advantageous to permit a certain restrictedamount of light absorption during the primary exposure with the effectthat the primary record is more pronounced (especially over the regionsreceiving only a small amount of light) towards the entrant side of theemulsion, with the result that the gamma in the higher density regionsof the finished relief becomes steeper, or in other Words, thecharacteristic H and D curve more concave upwardly. 'This effect will beeasily understood by considering that a certain light absorption duringthe making of record PL will leave the medium-to no-exposure partssomewhat recessed from the support, moving the corresponding parts ofline 1) towards the entrant surface, and therefore causing the upperdensity or high relief parts of the final relief to be exaggerated incomparison to the lower density or shallow parts thereof.

Still further, it-is evident that very thin emulsions of approximatelythe thickness of the highest parts of the finished relief can be used,resulting in an appreciable saving in emulsion material and a minimum ofdefinition loss due to halation in the primary exposure.

The modification illustrated in Fig. 3 utilizes for purposes of theinvention certain features of the well known so-called bichromate reliefprocesses. In carrying out this embodiment, a

positive record P may be made in emulsion E I printing thisnegativesilver record through the.

support, if under the given circumstances the projecting printingthereby involved is less onerous than the reversal process.

The emulsion E is then impregnated with a bichromate solution, forexample, potassium bichromate, according to any one of the many wellknown methods for making light sensitive bichromate emulsions.Preferably, the potassium bichromate bath is for the present purposemade rather more alkaline than normal, by adding some ammonia or otheralkali. The emulsion 13" containing silver record RN, and rendered lightsensitive throughout its thickness, is then exposed to uniform lightthrough the support. The record. RN controls this exposure, and wherethe bichromate gelatine is exposed to this light, it is renderedinsoluble according to well known principles. Hence, the region RPbetween line C and the support is hardened by the uniform secondaryexposure light controlled by record RN.

The film is then treated with hot water in the usual manner, dissolvingthe unexposed and therefore unhardened gelatine portions between line Cand the outer surface, the result being a gelatine relief R representinga positive record.

It should be especially noted that this proce- I dure obviates thedifficulty connected with all bichromate processes, namely the fact thatbichromated gelatine is relatively slow in its exposure reaction tolight, wherefore it has been heretofore impracticable to use it inmotion picture printing of the usual type. With the new method, thesecondary exposure can be made to any convenient light source withoutrestrictions concerning registration and time such as are imposed bymotion picture printing machines.

As already mentioned, the process introduces a new principle in theformation of a gelatine relief according to which the production of therelief depends primarily upon absorption of'light by the picture imagecontained within the gelatine layer itself, rather than by a generalabsorption of light in the film layer. -It follows, therefore, that thecontrast of the gelatine relief image is directly determined by that ofthe silver image, although this contrast can be reduced in linearproportions, that is, undistorted, by increasing the concentration ofthe bichromate, using relatively short-wave printing light, and by otherwell known methods.

It will now be evident that, instead of using for the primary exposuredyed emulsions and contrast light, as assumed for the process accordingto Fig. 3, undyed emulsions and penetrating exposure light ofsubstantially emulsion color can be used similar as described inconnection with Fig. 2. In this case, the process has the form asillustrated in Fig. 4, which will now be understood without detailedexplanation. In this figure, M is a master positive and F an undyedemulsion receiving a primary exposure to penetrating light resulting inaprimary latent record TN representing a negative.

Record TN is then developed, sensitized with bichromate, if desired dyedwith a light restraining' dye and resensitized emulsion F subjected tothe secondary exposure through the primary record. The secondaryexposure being effective between support and line (1, the result ofdevelopment in water is a relief R, representing a positivecorresponding to master positive M.

It will now be understood that the new process lends itself to manymodifications making use of one or the other of the'many techniquesknown in the photographic art for obtaining relief yielding records, thenovel basic idea being always the relief formation through lightabsorption by the picture record, contained within the emulsion itselfin effect nearthe emulsion side from which the secondary exposure lightenters,

rather than by .a general absorption of light in the film layer. Withthis procedure, the contrast of the gelatine relief is directlydetermined by that of the primary image, and not inversely as in thecase of the customary reversal processes where the primary record issubstantially near the emulsion side opposite to the surface whence thesecondary exposure light enters.

It will'also be evident to those skilled in the art that the hereindescribed embodiments of the invention are not restricted toexposureseither penetrating essentially the entire emulsion or to exposuressubstantially limited to the surface regions of the emulsion, but thatthe exposures may, and practicallyalways will have both characteristicsmixed, since these extreme types are more or less theoretical and cannot be perfectly obtained in actual practice. However, the exposureswill have the one, or the other character to a smaller or larger degree,which may be controlled depending upon the prevailing circumstances andthe desired character of the final relief record.

It should be understood that the present disclosure is for the purposeof illustration only, and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

What is claimed is:

1. The method of photographically producing gelatine reliefs whichcomprises the exposure of a silver haloid emulsion with light towhichsaid emulsion is sensitivebut which is only slightly absorbedtherein, thereby providing a primary silver record includingsubstantially all larger grains of said emulsion developing saidemulsion,.

throughout its entire thickness, maintaining the v emulsion sensitivesubstantially throughout its entire thickness, exposing the emulsionthrough its support under photographic exposure control by said primaryrecord, with light colored to be easily absorbed by said emulsion,thereby providing a secondary record concentrated near said supportwhereby the rate of contrast of the primary and secondary records iscontrolled by means of the primary exposure and of the adjustment of thelight absorption during the secondary exposure, hardening the gelatinecoextensive with said secondary record and substantially removing theunhardened gelatine, thereby providing a comparatively smooth gelatinerelief.

2. The method of photographically producing primary record, with lightof said range, thereby providing a secondary record concentrated nearsaid support whereby the rate of contrast of the primary and secondaryrecords is controlled by 7 means of the primary exposure and of theadjustment of the light absorption during the secondary exposure,hardening the gelatine coextensive with said secondary record andsubstantially removing the unhardened gelatine,

thereby providing a comparatively smooth gelatine relief.

3. The method of photographically producing gelatine reliefs whichcomprises the exposure of a silver haloid emulsion with light to whichsaid emulsion is sensitive but which is only slightly absorbed therein,developing said emulsion in a nonhardening developer to a comparativelyhigh rate of contrast thereby providing a silver record'includjngsubstantially all larger grains of said emulsion throughout its entirethickness, bleaching the developed emulsion and dyeing it with dye whichabsorbs light to which the emulsion is sensitive, exposing the saidemulsion through its support to light strongly absorbed by said dye,developing said emulsion in a hardening developer, bleaching saidemulsion, and removing the unhardened gelatine.

4. The method of photographically producing gelatine reliefs whichcomprises the exposure of a silver haloid emulsion with light which isonly slightly absorbed by said emulsion, developing said emulsionthereby providing a primary silver record including substantially alllarger grains of said emulsion throughout its entire thickness,sensitizing the emulsion with bichromate, exposing the emulsionsubstance through its support under photographic exposure'control bysaid primary record, with light colored to be easily absorbed by saidemulsion, thereby providing a secondary record concentrated near saidsupport whereby the rate of contrast of the primary and secondaryrecords is controlled by means of the primary exposure and of theadjustment of the light absorption during the secondary exposure, andsubstantially removing the gelatine not hardened by the exposure of thebichrornate sensitized gelatine, thereby providing a comparativelysmooth gelatine relief.

CAMBRIDGE TRUST COMPANY, Executor of the Last Will and Testament ofLeonard T. Troland, Deceased,

By S. MEAD WHEELER,

Its Asst. Secy.

